Process for recovery of by-products from waste pickle liquors



w. w. HODGE 2,322,134

PROCESS FOR RECOVERY OF' BY-PRODUCTS FROM WASTE PICKLE LIQUORS June 15,1943,

Filed Sept. 29, 1959 @FFSS m2 3G90 INVENTOR idd/Mx d #da Patented June.15, 1943 PROCESS FOR RECOVERY OF BY-PRJODUCTS FROM WASTE PICKLE LIQUORSWillard W. Hodge, Pittsburgh, Pa., assignor to Mellon Institute ofIndustrial Research,4 as trustee, a corporation of PennsylvaniaApplication September 29, 1939, Serial No. 297,133

2 Claims.

This invention relates to the pickling of metal; and consists in thereclaiming of spent pickling solutions by means of specific reagents toeiect replacement of the solute. It is characteristic (Cl. .Z3-126)(Within minutes) settle to the bottom of the ask. 'I'hesupernatantliquor is carefully decanted; the precipitate is subjected tofiltration on a. Bchner funnel with the aid of vacuum,

of such operations of regeneration that the re- 5 and the liquor isseparated and added to the placed solute may be recovered, and suchvalue decanted liquor.y 'p l as it possesses may be realised; and thatthe solu- The precipitate, taken from the Bchner funnel tion may berendered serviceable again. This is pressed between dry lter papers,then air dried invention lies in the discovery of particular refor about1 hour, until the odor'of -acetone is agents that have' peculiar utilityin the premises, l0 -no longer noticeable. Analysis will then show thein that by their employment spent pickling soluprecipitate to be eitherferrous sulfate pentations may with great facility be reclaimed, andhydrate, known as siderotilate, FeSO45HzO, or in that, afterreclamation, the solutions are the heptahydrate, FeSO47H2O, known ascophighly eective. Their eiectiveness is not imperas. paired because ofsuch trace or residue cf the The decanted liquor, Without any additionof reagent as may remain unreacted within them. fresh acid, will attackan article of iron immersed The accompanying drawing is diagrammatic. init. This decanted liquor, under distillation It is a flow-sheet,illustrative of practice under at atmospheric pressure, will render up alarge the invention. 1 portion ofthe acetone initially introduced. TheIn the steel mills pickling with dilute sulfuric residual liquor, aftersuch distillation, will be acid is common practice. The picklingoperation found to be of a specific gravity exceeding l, and involves areaction whose product is iron sulfate. to be strongly acid in reaction.The iron sulfate as it is formed goes vinto solu- If, instead ofproceeding at room temperature, tion in the pickling bath. As the bathcontinues the mixture 'of spent pickle liquor and acetone in use theiron sulfate accumulates within it to be maintained for several hours ina cold room the point where the correspondingly enfeebled (2 C.),it`wi1lbe found that about half the quanacid ceases to be effective. Theproposal has tity of acetone (125 cc.) will be eective, to pref beenmade, though without practical eiect, to cipitate most of the ironsulfate. Y reclaim such a pickling bath, when spent, by If, under theconditions of procedure rst adding to it a reagent that, by replacement,shall 39 given, the' quantity of acetone be reduced, afprerelease thedissolved iron sulfate. By my invencipitate may be gained that,onanalysis', will be tion that proposal is made eifective. found to besubstantially ferrous sulfate hepta- I have-found that, by adding tosuch a spent hydrate, FeSO4.7H2O-that is to say, copperas or picklingbath as that described acetone, green vitriol. (CHBMCO 35 In place ofacetone, I have found acetic acid, l CH3COOH,'to be serviceable, andwith this adin DIOper quantity, Substitution Will OCCHI. and vantage:that, whereas acetone in excess 'and the iron Sulphate, replaced in theSOllltOIi, Will unremoved does not restrain the activity of the bepreipitated and Will Separate by gravity; th@ residual sulfuric acid insolution; acetic acid, altered solution may readily be decanted; the 40similarly present, contributes positively to the still unreacted acid ofthe bath will be found to. effectiveness of the residual sulfuric acid.possess new eiicacy; and in the renewed pickling other reagents that 1have found to be eee Operation the new solute formed by SubstitlltOntive are acetaldehyde, propionic acid, and ethyl will be found t0 befree Of prejudicial GTBCD- Both acetate. All these substances are Watersoluble the released iron sulfate and the residual acetone or may bemade water Soluble by wending they may be recovered. are members of aclass of organic compounds OperatiOn may be COYlddCted 0n labl'aiOryknown as ketones, aldehydes, esters, and acids scale as follows:containing the carbonyl radical,

To 250 cc. waste pickle solution iii a 1 litre flask 250 cc. of acetoneare added. Both liquids are \C0 at the time at room temperature (29 C.).The y n liquids are thoroughly mixed by shaking. Almost A11 theWater-soluble members of this group that immediately an abundant crop oflight bluish I have tried I have found to be eil'ective to ac greencrystals appears; and a slight -'ise in tem`4 complish my end; and myexperiments lead me perature will be noted. The crystals quickly to theconclusion. that all ketcnes, aldehydes,

esters, and acids that contain the carbonyl group and that are watersoluble or those that may be made water soluble by addition of ablending solvent (for example acetone or ethyl alcohol) are soeffective. These solutes may be used singly or mixtures of them may beused.

In like manner and with like effect these reagents may be added to spentpickling solutions generally. The accompanying drawing consists of aflow-sheet of the procedure of the invention. Referring to the drawing,the waste pickle liquor is pumped from the pickling Vat, or from astorage sump below the vat, into the settling tank in winch anysuspended solid particles 'such as scale, rust, and dirt are settledout. The sensible heat in the spent pickle liquor may be used to preheatthe recovered dilute acid which is pumped from the storage sump locatedbelow the still; 4thisoperation may aid in rapidly cooling the wastepickle liquor in the settling tank and so reduce the amount of coolingrequired in the crystallizer; or the waste pickle liquor or therecovered acid may be used to preheat the mother liquor in storage tank.

When the waste pickle liquor has become sufficiently clarified andcooled in the settling tank, the liquor is drawn into the crystallizer,and if necessary is then further cooled to a satisfactory temperaturefor the addition of the required quantity of differential solute. Thesolute is pumped from storage tank and is mixed with the clarified wastepiclde liquor by means of the -stirrer in the crystallizer; or thesolute may be pumped into the crystallizer first and the waste pickleliquor allowed to flow into it, so that mixing takes place by gravityand splash and no stirrer is needed. The temperature of the mixture inthe crystallizer is controlled by means of cooling brine circulating incoils or jackets installed in or on the crystallizer; If power andrefrigeration are cheap it will be advisable to cool the mixture in thecrystallizer to low temperature, perhaps to 1 to 2 C., but ifrefrigeration be costly itwill be more economical to use a largerproportion of the differential solute and perform less cooling of themixture in the crystallizer. 'I'his is a matter of relative costs andmust be considered in connection with the costs for steam to heat thestill for the recovery of the differential solute and the proportion ofsolute recoverable to that consumed in the substituent operation.

After the acetone and waste pickle liquor have been mixed in thecrystallizer, the stirrer is stopped and the crystals of iron sulphatesettle rapidly into the cone-shaped bottom of the crystallizer. Theclear supernatant mother liquor is drawn oi from the crystallizer intothe mother liquor storage tank. The magma of crystalline precipitate isdrawn from the bottom of the crystallizer into a centrifuge or filter,in which the precipitate is separated from the remaining mother liquor,which is then pumped into the mother liquor storage tank. Theprecipitate goes from the centrifuge or filter into a storage bin, or itmay go directly to a dryer, in which the traces of mother liquoroccluded on the surfaces of the crystals are driven oi and theprecipitate may be dried to whichever hydrate of iron sulfate isdesired. In practice it will in some cases be desirable to install asolute recovery tower, to strip the solute from the exit gases from thedryer, depending on which differential solute or mixture is used in theprocess and the quantity of it remaining with the precipitate when thematerial enters the dryer. After leaving the dryer the precipitate isconveyed to storage bins for packing and sale, or to be used in themanufacture of other products, such as sulfuric acid and iron oxide,ammonium sulfate or other sulfates, wall-board, building blocks, andother usable materials.

The mother liquor in storage in tank may be preheated to a temperaturesatisfactory for feeding to the correct plate of the fractionatingcoiumn of the still, and distilled or evaporated, and the vaporscondensed and recovered. The preheating of the mother liquor in the tankmay be accomplished by circulating through the heat exchanger coils inthe tank the hot dilute acid discharged from the bottom of the still, orwaste pickle liquor from the pickling vat or sump. The differentialsolute or mixture recovered by distillation and condensation in stilland column and condenser flows into the tank for solute storage. Thisrecovered solute may be pumped from tank into crystallizer and used overagain, as required for the operation of the process. The water andsulfuric acid are reiiuxed down the fractionating column and collect inthe bottom of stillI from which they are drawn into the storage sump.This hot dilute acid may be pumped through heat exchanger coils orjackets in the mother liquor storage tank and the waste pickle liquorsettling tank before flowing into storage tank, or the recovered diluteacid solution may be pumped directly to this storage tank. 'I'herecovered acid may be used with the addition to it of the correctproportion of fresh concentrated sulfuric acid. due caution beingexercised in adding the concentrated acid, in making up the picklingsolution for use in the picklers. 'I'he recovered acid may be used forother purposes.

The procedure as above described is of the nature of a batch operation.Howeverl the flow sheet for the process may be easily modified and theplant design and equipment readily changed to adapt the process tocontinuous operation, if that system is better adapted to the picklingoperations in the metallurgical plant.

I have in this specification described the regeneration of spentsolutions that have been used in the pickling of steel articles,particularly. The invention is of wide and general utility, and may bepractised upon the spent solutions of copper and brass picklingoperations. for example, and the liquors resulting from the leeching ofores with sulphuric, hydrochloric, or other mineral acids.

In the flow sheet here presented the reuse of the recovered acid in thepickling operation is indicated. However, this recovered acid may beused for other purposes, and it is not the intent of this invention tolimit the uses to be made of the recovered acid or other recoveredby-products. Experiments have been carried out in which some of therecovered acid was neutralized with ammonium hydroxide; the precipitateformed' was easily separated by settling and filtration. The

lfiltrate was evaporated and ammonium sulfate used in sewage treatment,water purification, and

for the manufacture of glass polishing rouge and paint pigments. Also,these compounds have some uses as insecticides.' fungicides, and weedkillers. The ferrous sulfate heptahydrate could also be used in themanufacture of wall-board, building blocks, and other buildingmaterials.

The ferrous sulfate monohydrate, FeSO4.1 Vgl-120. or with less water ofhydration is the ferrousl which the waste pickle liquors may be kept outof the streams, thus reducing stream pollution; and, as has been said,produces from the waste pickle liquors valuable usable by-products.

In this application the operation of my inven- `tion is illustratedusing the waste liquor from pickllng ferrous metals, as an example.However, the invention is also applicable to liquors containing othermetals as sulfates, such as copper sulfate, nickel sulfate, zincsulfate, aluminum sulfate, and sodium sulfate.

I claim as my invention: A

l. 'Ihe method of reclaiming spent pickling solution containing ferroussulfate which comprises eiecting precipitation of ferrous sulfate fromcold spent pickling solution by the addition producing more sulfuricacid .and also reddish brown deposits of ferric compounds on the banksof the streams. 'Ihe rates of corrosion of the metallic Darts of boats.barges, pipe lines, locks, and bridges are greatly increased by the acidwater in streams. 'Ihis process presents a method by of acetone, andseparating the precipitate.

2. The method of reclaiming spent pickli-ng solution containing ferroussulfate which comprises effecting precipitation of ferrous sulfate fromcold spent pickling solution by the addition of a watersoluble ketone,and separating the precipitate.

WILLARD W. HODGE.

